Near-infrared Laser Absorption Spectroscopy Research Articles

Near-Infrared Laser Methane Remote Monitoring Based on Template Matching Algorithm of Harmonic Signals

Trustworthy technology for the monitoring of fugitive methane emissions is an indispensable component for low−carbon emission reduction and safe production in oil and gas infrastructure. A miniaturization and low-cost methane remote monitoring prototype based on near-infrared laser absorption spectroscopy is developed to retrieve the path−integral concentration by employing the harmonic conjoint analysis method for the backscattered echo signals from a distant non-cooperative target. A distorted harmonic template matching (DHTM) algorithm is proposed based on wavelength modulation spectroscopy with second harmonic normalized via the first harmonic (WMS−2f/1f) method, which suppresses the output concentration fluctuation caused by open path monitoring with non-cooperative target and avoids the issue of false alarms during the detection process without target gas. The reliability of the WMS−2f/1f−DHTM algorithm is verified by calibration and dynamic experiments. The results showed that this algorithm avoids the dilemma of false alarms in the absence of gas compared to the conventional WMS−2f/1f algorithm, while the root mean square error (RMSE) of the concentration inversion with a detection distance of 20 m is reduced by 57.6% compared to direct absorption spectroscopy (DAS) algorithm. And the minimum detection limit of system is 3.79 ppm·m. The methane telemetry sensor with the WMS−2f/1f−DHTM algorithm exhibits substantial application potential in carbon monitoring of oil and gas industry.

A sensitive carbon monoxide sensor for industrial process control based on laser absorption spectroscopy with a 2.3 μm distributed feedback laser

Carbon monoxide (CO) is a ubiquitous atmospheric trace gas produced by natural and anthropogenic sources. It can be used as a quantitative marker to help us understand the different production processes. A near-infrared laser absorption spectroscopy of 2.3 μm based in-situ, real-time and continuous CO sensor equipment is developed for the exhaust pipeline of furnace. High sensitivity is accomplished utilizing the ratio between the second and first harmonic signals detection (WMS-2f/1f). The analyzer is housed in an explosion-proof enclosure and installed at both sides of the pipeline with a diameter of 2.1 m. The measured gas temperature inside the pipeline reaches around 400 K. The results primarily show a more linear response and less error, the measurement precision and the minimum detection limit are 0.42 ppm and 1.29 ppm (1σ), simultaneously. Evaluation of the data suggested a dynamic range from 3.87 ppm to 1.3% based on the 3σ rule and maximum absorbance of one. An operator can analyze the industrial production process clearly, that is, the measured CO concentration is negatively correlated with excess oxygen (O2) by observing the measurement results within 10 h. Meanwhile, the measurements of the real targets show that the sensor has great applicability and potential for exhaust pipeline and combustion control systems.

A methane telemetry sensor based on near-infrared laser absorption spectroscopy

In order to detect methane leakage accurately and prompt, a methane telemetry sensor is demonstrated based on near infrared absorption spectroscopy and optimized wavelength modulation technology. The distributed feedback diode laser is applied as the light source to cover the selected absorption line of 6046 cm−1 to reduce the interference of CO2 and H2O. The waveform generator and the digital quadrature lock-in amplifier are constructed by the FPGA to produce driving signals and extract WMS-1f and 2f signals. And the “2f/1f” method is adopted to eliminate the environment influence such as light intensity fluctuations and improve the signal-to-noise ratio. This methane sensor has the characteristics of fast response and strong resistance to environmental interference and has great application prospect.

A numerical simulation of a near-infrared three-channel trace ammonia detection system using hollow core photonic crystal fiber

A simulation model of the fiber-structure trace ammonia detection system based on near-infrared laser absorption spectroscopy is proposed. The distributed feed-back (DFB) diode laser modulation, photodetector, and signal processing are simulated by programming using matlab code while the noise amplitude selected to the sampling accuracy of commercial 12-bit ADC. The wavelength 1512 nm was selected to calculate the absorption coefficient of mixture containing ammonia, carbon dioxide, and water vapor. When the length of fiber-structure gas chamber was set to 10 cm, 1 m, and 10 m, respectively, ammonia with concentration from 0.2 ppm to 10,060 ppm can be detected. The dynamic range of this simulation have covered 5 orders of magnitude which never achieves in traditional detection system. Our work provides a potentially valuable option to establish the ammonia detection system of more portable, high sensitivity, and large detection range.

A portable sensor for in-situ measurement of ammonia based on near-infrared laser absorption spectroscopy

A portable laser sensor for trace ammonia (NH3) is developed based on near-infrared laser absorption spectroscopy. Tunable diode laser absorption spectroscopy in conjunction with wavelength modulation spectroscopy is implemented by a system-on-chip based on field-programmable gate array. A variable temperature multipass cell with a 15 m optical path length is adopted to enhance the absorption path length and avoid the NH3 adsorption. The physical dimension of the sensor is minimized into 43 × 18 × 16 cm3 on the benefit of home-made electronic system and compact optical design. A unique absorption line of NH3 around 1.51 µm covered by a distributed feedback diode laser is selected to reduce the influence from carbon dioxide, vapor and other trace gases. Calibration-free modulation spectroscopy is employed to avoid the random fluctuations due to laser noise and non-absorption transmission losses. The performance of sensor including adsorption of NH3, stability and flow of gas are examined and discussed in detail. For removing the adsorption of NH3, the temperature-dependent curve is obtained by the direct absorption spectroscopy, and it shows that the adsorption is significantly suppressed at (or higher than) 415 K. According to Allan deviation analysis, the minimum detection limit is 0.16 ppm at 184 s, and the rise time and the fall time of system are about 4.5 s and 3.7 s, respectively. The feasibility of the sensor is validated and deployed to monitor the NH3 slip in selective catalytic reduction (SCR) of coke oven flue gas. The work provides a potentially valuable control sensor for SCR.

Highly sensitive detection of methane by near-infrared laser absorption spectroscopy using a compact dense-pattern multipass cell

Highly sensitive detection of atmospheric methane (CH4) was performed by long optical pathlength absorption spectroscopy based on a novel compact dense-pattern multipass cell (DP-MPC) in conjunction with a fiber-coupled distributed feedback diode laser operating at 1.653μm. Wavelength modulation spectroscopy approach was used and a minimum detectable concentration (1σ) of 100ppb was obtained with a lock-in time constant of 1ms. A measurement precision of <79ppb was achieved by average of five laser scans in 1s. This newly developed DP-MPC realized 215 times multiple reflections between two very cheap and robust silver coated concave spherical mirrors separated by a distance of 12cm (forming an absorption cell of 280cm3 volume), offering an effective optical path length of 26.4m, which is very suitable for applications to trace gas sensing in harsh environment, and weight-limited unmanned aerial vehicle (UAV) – or balloon-embedded field observations.

Two-Dimensional Imaging of Water Vapor by Near-Infrared Laser Absorption Spectroscopy

Both a flow of water vapor generated from a humidification device and stable water vapor at constant moisture were successfully visualized by near-infrared (NIR) laser absorption spectroscopy. Two different types of optical arrangement for two-dimensional (2D) imaging, i.e., one-wavelength reflection and two-wavelength transmission, were tested. A flow of water vapor within a wide view range was clearly visualized by the former, while low content of stable water vapor was quantitatively detected by the latter. It was demonstrated that a detection limit of 0.8 g.m(-3) was achieved by means of the 2D-NIR imaging system developed in the present study.

有機金属化学気相成長装置内の表面吸着水の高速除去

The chambers of Metal Organic Chemical Vapor Deposition (MOCVD) equipment are opened at regular intervals, in order to remove the by-products on the inner surface of the reactor chambers. After regular maintenance, it is difficult to remove water molecules adsorbed on the inner surface of chambers, so the through-put of wafers is difficult to improve. The purpose of this work is to present the method to remove adsorbed water molecules on the inner surface of chambers quickly. For this purpose, we use an in-situ and real-time moisture monitor based on near-infrared laser absorption spectroscopy and continuously measure the moisture concentration in MOCVD equipment exhaust gases at the experiment. It was clarified that the baking efficiency is improved by using the high thermal conductivity gases such as hydrogen (H2) gas and that the purge time is shorten by introducing trimethylaluminum (TMA) to purge gas under room temperature condition.

Near-infrared laser absorption spectroscopy of the CS + cation

The (1, 0) band of the A 2 Π– X 2 Σ + transition of the CS + cation has been measured in absorption at Doppler-limited resolution, between 12 400 and 13 000 cm −1. The spectrum was recorded using differential velocity modulation detection and a Ti: sapphire laser as the near-infrared light source. The v=1 A 2 Π upper state of the band is perturbed by the v=10 level of the ground state. A deperturbation analysis using >300 rotational lines was carried out to derive accurate ground- and upper-state parameters. The ground-state rotational and fine-structure constants are in very good agreement with those from a Fourier transform emission study in which the ground-state constants were derived from combination differences.